But the astronomical carnage continues

There is only one thing more deadly to birds than buildings – cats!

Research by the Green Building Alliance (GBA), a US-based group of architects, engineers and designers of environmentally sustainable projects, says cats are the only things that kill more birds than building collisions.

The group reckons power lines in the US kill 100 – 200 million birds annually, and wind turbines account for another 10,000 – 40,000.

But the biggies are buildings (mainly glass-clad) and moggies (domestic and feral) – each taking out up to one billion birds a year. And that’s just in the United States.

Shocking figures

These are shocking and little known figures, and dwarf the more highly publicised numbers associated with migratory wading bird losses to habitat destruction and climate change. (Of course, there are far fewer waders on the planet than there are general bird species, so the net impact on the former would be greater.)

Virtually any building with glass poses a threat to birds. Yes, even in the architecturally challenged tropical Australian city of Cairns (the writer’s adopted home), bird strike is apparently a problem.

Passionate Cairns birding identity Brian Venables has blamed the reflective surfaces of the city’s Botanical Gardens Visitor Centre for the recent death of two little kingfishers (Ceyx pusillus). An iconic species in the area, he believes the kingfisher fatalities are part of a string of incidents involving a variety of species.

While the likes of Venables highlight the problem at the local level, we Natural Images has uncovered evidence of significant new research and advances in the creation of more bird-friendly buildings.

The GBA says birds have poor depth perception and can’t distinguish architectural context clues that humans use to avoid collisions. Reflections on glass can also make a building or window appear similar to nearby vegetation or the rest of the sky, causing birds to think that is a safe place to fly.

“When glass looks transparent,” says the GBA, “birds may want to fly to whatever is behind it, particularly if there is indoor foliage. Glass often appears transparent when it is used for railings, skywalks, or on both sides of the corner of a building.”

Lower levels crucial

The organisation says the lower levels of a building (first 12 m) and levels next to a green roof are places where bird-friendly design is most critical.

The GBA says wildlife biologists have tested bird-deterring windows using a dark tunnel with a window at one end. Half the window is a pane of the glass being tested and next to it is a standard pane of clear glass. A bird placed in the tunnel will fly towards the window to try to escape and is stopped with netting before reaching the window—but allowing researchers to see which side it favours.

A significant preference for clear glass indicates that birds perceive the other pane of glass as an obstacle, which is exactly what is needed for bird-friendly design.

New glass technology that birds can see is coming on the market

Horizontal spaces

The study has also confirmed that most birds will only fly through horizontal spaces 50 mm or higher and vertical spaces 100 mm or wider. Therefore, window patterns should have empty spaces no larger than 50 mm x 100 mm as an effective deterrent.

New York City architect Guy Maxwell(How to Make a Bird-Friendly Building), confirms that the size of the glass and the amount of reflected vegetation or cloud are the major factors causing collision.

Glass wrapped around corners is another problem: “[Because] the bird can see all the way through to the other side, it thinks it can fly right through.”

More architects are looking for new glass products that birds can see, and which also looks good to us. For instance, etched window glass looks like a blank wall to birds but humans can see through it just fine.

A pencil-thin ceramic embedded in or on the glass called ‘frit’ is another possibility. It definitely diverts birds, but only if the rows of frit are not more than 50 mm apart. A German product featuring chaotic patterns of lines painted inside the glass (rather like the pick-up sticks game) is apparently showing good results.

And if all else fails, there are always wooden louvres!

Footnote: The powerful US Green Building Council’s Leadership in Energy and Environmental Design (LEED) program is taking pro-bird building design very seriously. Well known for awarding credits for embodied energy and the sustainable use of materials, LEED is now taking into account the bird-friendliness of materials, lighting, proximity to vegetation and bodies of water.